Capacitors are used in a number of different applications in integrated circuit devices. One application is as decoupling capacitors, which are used with large scale integrated circuits having a high number of driver circuits. Another application is as memory capacitors, which are used in integrated circuit memory cells having a high integration density and which use a combination of the transistor and the memory capacitor in a memory cell.
Capacitors are used in decoupling applications because the driver circuit power connections in integrated circuits are particularly sensitive to noise created by the effective inductance inherent in simultaneous switching activity as occurs with parallel processing. Further, the trend towards higher speed and lower power consumption of semiconductor devices, such as microcomputers and digital signal processors, has caused greater problems with electromagnetic interference or electromagnetic noise. The most effective measure against noise has been to use a decoupling capacitor so that the switching noise will not be coupled to a signal line through a common main power source circuit. Such a decoupling capacitor serves as a power source that can be easily utilized for switching the semiconductor element, such as a transistor. The decoupling capacitor is charged by an external power source and is rapidly discharged to give a switching current which minimizes electromagnetic noise. At the same time, the switching speed of the logic circuit is related to the inductance of the current path between the semiconductor element and the capacitor. In order to minimize the inductance and inductive noise, the semiconductor element and the capacitor must be arranged very close to each other, and a number of short current paths must be provided between the semiconductor element and the capacitor.
Semiconductor devices have been developed with decoupling capacitors disposed neighboring each of the semiconductor elements on the upper surface of the semiconductor substrate as one attempt to solve the problems associated with these decoupling capacitors but these arrangements continue to encounter problems as sizes shrink.
In the memory capacitor application, recent largecapacity DRAMs (Dynamic Random Access Memories) have to have stacked capacitor structures in which information-storing capacitors are arranged above memory-cell-selecting transistors. These stacked capacitor structures compensate for the decrease of accumulated charges because the memory cells are micro-miniaturized. Even with this reduction in the size of the memory cell, it is necessary to maintain the capacitance to insure stable operation, and as sizes shrink, the problems continue to return.
Numerous cylindrical capacitors have been developed for use in integrated circuits, but they are primarily based on modifications of the polysilicon structure and/or require a large number of steps in their manufacture. A high capacitance, easily manufactured capacitor for semiconductor devices and these applications have long been sought but has eluded those skilled in the art.